Conventional high gain aperture antennas, such as a parabolic reflector antenna, are widely used for millimeter-wave bands in different areas, because of their high gain, wide bandwidth and simple structure. However, these antennas have a large profile with regards to the beam direction, large size and relatively high cost. To overcome the drawbacks of conventional millimeter-wave high gain aperture antennas, different millimeter-wave planar aperture antennas, e.g., horn and horn-like antenna, using different planar circuit technologies have been proposed, but these designs suffer from either low gain or high cost.